Method of making organic electroluminescent materials

ABSTRACT

A method of forming compounds that comprise a heterocyclic carbene ligand is provided. In particular, an oxazole or a thioazole carbene are used in place of the traditional imidazole carbene. These compounds may be used in OLEDs to provide devices having improved properties, such as stability and color-tuning.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 13/033,287, filed Feb. 23, 2011, the entirety of which isincorporated herein by reference.

PARTIES TO A JOINT RESEARCH AGREEMENT

The claimed invention was made by, on behalf of, and/or in connectionwith one or more of the following parties to a joint universitycorporation research agreement: Regents of the University of Michigan,Princeton University, University of Southern California, and UniversalDisplay Corporation. The agreement was in effect on and before the datethe claimed invention was made, and the claimed invention was made as aresult of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention relates to organic light emitting devices (OLEDs).More specifically, the present invention is related to heterocycliccarbene metal complexes. These materials may be used in OLEDs to provideimproved stability and color-tuning.

BACKGROUND

Opto-electronic devices that make use of organic materials are becomingincreasingly desirable for a number of reasons. Many of the materialsused to make such devices are relatively inexpensive, so organicopto-electronic devices have the potential for cost advantages overinorganic devices. In addition, the inherent properties of organicmaterials, such as their flexibility, may make them well suited forparticular applications such as fabrication on a flexible substrate.Examples of organic opto-electronic devices include organic lightemitting devices (OLEDs), organic phototransistors, organic photovoltaiccells, and organic photodetectors. For OLEDs, the organic materials mayhave performance advantages over conventional materials. For example,the wavelength at which an organic emissive layer emits light maygenerally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage isapplied across the device. OLEDs are becoming an increasinglyinteresting technology for use in applications such as flat paneldisplays, illumination, and backlighting. Several OLED materials andconfigurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full colordisplay. Industry standards for such a display call for pixels adaptedto emit particular colors, referred to as “saturated” colors. Inparticular, these standards call for saturated red, green, and bluepixels. Color may be measured using CIE coordinates, which are wellknown to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure:

In this, and later figures herein, we depict the dative bond fromnitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as wellas small molecule organic materials that may be used to fabricateorganic opto-electronic devices. “Small molecule” refers to any organicmaterial that is not a polymer, and “small molecules” may actually bequite large. Small molecules may include repeat units in somecircumstances. For example, using a long chain alkyl group as asubstituent does not remove a molecule from the “small molecule” class.Small molecules may also be incorporated into polymers, for example as apendent group on a polymer backbone or as a part of the backbone. Smallmolecules may also serve as the core moiety of a dendrimer, whichconsists of a series of chemical shells built on the core moiety. Thecore moiety of a dendrimer may be a fluorescent or phosphorescent smallmolecule emitter. A dendrimer may be a “small molecule,” and it isbelieved that all dendrimers currently used in the field of OLEDs aresmall molecules.

As used herein, “top” means furthest away from the substrate, while“bottom” means closest to the substrate. Where a first layer isdescribed as “disposed over” a second layer, the first layer is disposedfurther away from substrate. There may be other layers between the firstand second layer, unless it is specified that the first layer is “incontact with” the second layer. For example, a cathode may be describedas “disposed over” an anode, even though there are various organiclayers in between.

As used herein, “solution processible” means capable of being dissolved,dispersed, or transported in and/or deposited from a liquid medium,either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed thatthe ligand directly contributes to the photoactive properties of anemissive material. A ligand may be referred to as “ancillary” when it isbelieved that the ligand does not contribute to the photoactiveproperties of an emissive material, although an ancillary ligand mayalter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled inthe art, a first “Highest Occupied Molecular Orbital” (HOMO) or “LowestUnoccupied Molecular Orbital” (LUMO) energy level is “greater than” or“higher than” a second HOMO or LUMO energy level if the first energylevel is closer to the vacuum energy level. Since ionization potentials(IP) are measured as a negative energy relative to a vacuum level, ahigher HOMO energy level corresponds to an IP having a smaller absolutevalue (an IP that is less negative). Similarly, a higher LUMO energylevel corresponds to an electron affinity (EA) having a smaller absolutevalue (an EA that is less negative). On a conventional energy leveldiagram, with the vacuum level at the top, the LUMO energy level of amaterial is higher than the HOMO energy level of the same material. A“higher” HOMO or LUMO energy level appears closer to the top of such adiagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled inthe art, a first work function is “greater than” or “higher than” asecond work function if the first work function has a higher absolutevalue. Because work functions are generally measured as negative numbersrelative to vacuum level, this means that a “higher” work function ismore negative. On a conventional energy level diagram, with the vacuumlevel at the top, a “higher” work function is illustrated as furtheraway from the vacuum level in the downward direction. Thus, thedefinitions of HOMO and LUMO energy levels follow a different conventionthan work functions.

More details on OLEDs, and the definitions described above, can be foundin U.S. Pat. No. 7,279,704, which is incorporated herein by reference inits entirety.

SUMMARY OF THE INVENTION

Heterocyclic carbene metal complexes are provided. The compoundscomprise a ligand L having the structure:

X₁ is S or O. X₂, X₃, X₄, and X₅ are independently C or N. At least oneof X₂, X₃, X₄, and X₅ is N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. Preferably, A is benzene.The ligand L is coordinated to a transition metal M having an atomicnumber greater than 40. Preferably, the metal M is Ir or Os. Morepreferably, the metal M is Ir. Additionally, the metal M is preferablyOs. The bidentate ligand L may be linked with other ligands to comprisea tridentate, tetradentate, pentadentate or hexadentate ligand.

In one aspect, the ligand has the formula:

At least one of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In another aspect, the ligand has the formula:

At least two of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In one aspect, the compound is heteroleptic. In another aspect, thecompound is homoleptic. In yet another aspect, the compound has theformula:

Specific examples of the heterocyclic carbene compounds are provided. Inone aspect, the compound is selected from the group consisting of:

Each X₁ is independently S or O.

Additional specific examples of heterocyclic carbene compounds areprovided. In one aspect, the compound is selected from the groupconsisting of:

Additionally, a first device comprising an organic light emitting deviceis provided. The organic light emitting device further comprises ananode, a cathode, and an organic layer, disposed between the anode andthe cathode. The organic layer comprises a compound comprising a ligandL having the structure:

X₁ is S or O. X₂, X₃, X₄, and X₅ are independently C or N. At least oneof X₂, X₃, X₄, and X₅ is N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. Preferably, A is benzene.The ligand L is coordinated to a transition metal M having an atomicnumber greater than 40. Preferably, the metal M is Ir or Os. Morepreferably, the metal M is Os. More preferably, the metal M is Ir. Thebidentate ligand may be linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

The various specific aspects discussed above for compounds havingFormula I are also applicable to a compound having Formula I when usedin the first device. In particular, the various specific aspects of X₁,X₂, X₃, X₄, X₅, R₁, R_(A), and A of the compound having Formula I, asdiscussed above, are also applicable to the compound having Formula Ithat is used in the first device.

Specific examples of compounds that may be used in the device areprovided. In one aspect, the compound is selected from the groupconsisting of Compound 1G-Compound 28G. Each X₁ is independently S or O.In another aspect, the compound is selected from the group consisting ofCompound 1-Compound 20.

In one aspect, the organic layer is an emissive layer and the compoundis an emissive dopant. In another aspect, the organic layer furthercomprises a host. Preferably, the host is a compound that comprises atleast one of the chemical groups selected from the group consisting of:

Each of R′″₁, R′″₂, R′″₃, R′″₄, R′″₅, R′″₆ and R′″₇ are independentlyselected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof. Two adjacentsubstituents of R′″₁, R′″₂, R′″₃, R′″₄, R′″₅, R′″₆ and R′″₇ areoptionally joined to form a fused ring. k is an integer from 0 to 20.Each of X¹, X², X³, X⁴, X⁵, X⁶, X⁷ and X⁸ are independently selectedfrom the group consisting of CH and N.

In another aspect, the host is a metal complex. In yet another aspect,the metal complex is selected from the group consisting of:

(O—N) is a bidentate ligand having metal coordinated to atoms O and N. Lis an ancillary ligand. m is an integer value from 1 to the maximumnumber of ligands that may be attached to the metal.

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

A process for making a carbene metal complex is also provided. Theprocess comprises reacting the copper dichloride carbene dimer with ametal precursor to yield the carbene metal complex. In one aspect, theprocess further comprises reacting a carbene salt with copper-t-butoxideto yield a copper dichloride carbene dimer, prior to reacting the copperdichloride carbene dimer with the metal precursor.

In one aspect, the metal is Ir, Os, Ru or Pt. In another aspect, themetal precursor is selected from the group consisting of [IrCl(COD)]₂,OsCl₂(DMSO)₄, RuCl₂(DMSO)₄, and PtCl₂(SEt₂)₂.

In one aspect, the carbene metal complex has the formula:

X₁ is NR_(B), S or O. In one aspect, X₁ is NR_(B). In another aspect, X₁is S. In yet another aspect, X₁ is O. X₂, X₃, X₄, and X₅ areindependently C or N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. R_(B) is selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. The ligand L iscoordinated to a transition metal M having an atomic number greater than40. The bidentate ligand may be linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

In one aspect, the carbene metal complex is heteroleptic. In anotheraspect, the carbene metal complex is homoleptic. Preferably, the carbenemetal complex is tris configuration.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does nothave a separate electron transport layer.

FIG. 3 shows a heterocyclic carbene metal complex.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed betweenand electrically connected to an anode and a cathode. When a current isapplied, the anode injects holes and the cathode injects electrons intothe organic layer(s). The injected holes and electrons each migratetoward the oppositely charged electrode. When an electron and holelocalize on the same molecule, an “exciton,” which is a localizedelectron-hole pair having an excited energy state, is formed. Light isemitted when the exciton relaxes via a photoemissive mechanism. In somecases, the exciton may be localized on an excimer or an exciplex.Non-radiative mechanisms, such as thermal relaxation, may also occur,but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from theirsinglet states (“fluorescence”) as disclosed, for example, in U.S. Pat.No. 4,769,292, which is incorporated by reference in its entirety.Fluorescent emission generally occurs in a time frame of less than 10nanoseconds.

More recently, OLEDs having emissive materials that emit light fromtriplet states (“phosphorescence”) have been demonstrated. Baldo et al.,“Highly Efficient Phosphorescent Emission from OrganicElectroluminescent Devices,” Nature, vol. 395, 151-154, 1998;(“Baldo-I”) and Baldo et al., “Very high-efficiency green organiclight-emitting devices based on electrophosphorescence,” Appl. Phys.Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporatedby reference in their entireties. Phosphorescence is described in moredetail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporatedby reference.

FIG. 1 shows an organic light emitting device 100. The figures are notnecessarily drawn to scale. Device 100 may include a substrate 110, ananode 115, a hole injection layer 120, a hole transport layer 125, anelectron blocking layer 130, an emissive layer 135, a hole blockinglayer 140, an electron transport layer 145, an electron injection layer150, a protective layer 155, and a cathode 160. Cathode 160 is acompound cathode having a first conductive layer 162 and a secondconductive layer 164. Device 100 may be fabricated by depositing thelayers described, in order. The properties and functions of thesevarious layers, as well as example materials, are described in moredetail in U.S. Pat. No. 7,279,704 at cols. 6-10, which are incorporatedby reference.

More examples for each of these layers are available. For example, aflexible and transparent substrate-anode combination is disclosed inU.S. Pat. No. 5,844,363, which is incorporated by reference in itsentirety. An example of a p-doped hole transport layer is m-MTDATA dopedwith F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. PatentApplication Publication No. 2003/0230980, which is incorporated byreference in its entirety. Examples of emissive and host materials aredisclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which isincorporated by reference in its entirety. An example of an n-dopedelectron transport layer is BPhen doped with Li at a molar ratio of 1:1,as disclosed in U.S. Patent Application Publication No. 2003/0230980,which is incorporated by reference in its entirety. U.S. Pat. Nos.5,703,436 and 5,707,745, which are incorporated by reference in theirentireties, disclose examples of cathodes including compound cathodeshaving a thin layer of metal such as Mg:Ag with an overlyingtransparent, electrically-conductive, sputter-deposited ITO layer. Thetheory and use of blocking layers is described in more detail in U.S.Pat. No. 6,097,147 and U.S. Patent Application Publication No.2003/0230980, which are incorporated by reference in their entireties.Examples of injection layers are provided in U.S. Patent ApplicationPublication No. 2004/0174116, which is incorporated by reference in itsentirety. A description of protective layers may be found in U.S. PatentApplication Publication No. 2004/0174116, which is incorporated byreference in its entirety.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210,a cathode 215, an emissive layer 220, a hole transport layer 225, and ananode 230. Device 200 may be fabricated by depositing the layersdescribed, in order. Because the most common OLED configuration has acathode disposed over the anode, and device 200 has cathode 215 disposedunder anode 230, device 200 may be referred to as an “inverted” OLED.Materials similar to those described with respect to device 100 may beused in the corresponding layers of device 200. FIG. 2 provides oneexample of how some layers may be omitted from the structure of device100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided byway of non-limiting example, and it is understood that embodiments ofthe invention may be used in connection with a wide variety of otherstructures. The specific materials and structures described areexemplary in nature, and other materials and structures may be used.Functional OLEDs may be achieved by combining the various layersdescribed in different ways, or layers may be omitted entirely, based ondesign, performance, and cost factors. Other layers not specificallydescribed may also be included. Materials other than those specificallydescribed may be used. Although many of the examples provided hereindescribe various layers as comprising a single material, it isunderstood that combinations of materials, such as a mixture of host anddopant, or more generally a mixture, may be used. Also, the layers mayhave various sublayers. The names given to the various layers herein arenot intended to be strictly limiting. For example, in device 200, holetransport layer 225 transports holes and injects holes into emissivelayer 220, and may be described as a hole transport layer or a holeinjection layer. In one embodiment, an OLED may be described as havingan “organic layer” disposed between a cathode and an anode. This organiclayer may comprise a single layer, or may further comprise multiplelayers of different organic materials as described, for example, withrespect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used,such as OLEDs comprised of polymeric materials (PLEDs) such as disclosedin U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated byreference in its entirety. By way of further example, OLEDs having asingle organic layer may be used. OLEDs may be stacked, for example asdescribed in U.S. Pat. No. 5,707,745 to Forrest et al, which isincorporated by reference in its entirety. The OLED structure maydeviate from the simple layered structure illustrated in FIGS. 1 and 2.For example, the substrate may include an angled reflective surface toimprove out-coupling, such as a mesa structure as described in U.S. Pat.No. 6,091,195 to Forrest et al., and/or a pit structure as described inU.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated byreference in their entireties.

Unless otherwise specified, any of the layers of the various embodimentsmay be deposited by any suitable method. For the organic layers,preferred methods include thermal evaporation, ink-jet, such asdescribed in U.S. Pat. Nos. 6,013,982 and 6,087,196, which areincorporated by reference in their entireties, organic vapor phasedeposition (OVPD), such as described in U.S. Pat. No. 6,337,102 toForrest et al., which is incorporated by reference in its entirety, anddeposition by organic vapor jet printing (OVJP), such as described inU.S. patent application Ser. No. 10/233,470, which is incorporated byreference in its entirety. Other suitable deposition methods includespin coating and other solution based processes. Solution basedprocesses are preferably carried out in nitrogen or an inert atmosphere.For the other layers, preferred methods include thermal evaporation.Preferred patterning methods include deposition through a mask, coldwelding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819,which are incorporated by reference in their entireties, and patterningassociated with some of the deposition methods such as ink jet and OVJD.Other methods may also be used. The materials to be deposited may bemodified to make them compatible with a particular deposition method.For example, substituents such as alkyl and aryl groups, branched orunbranched, and preferably containing at least 3 carbons, may be used insmall molecules to enhance their ability to undergo solution processing.Substituents having 20 carbons or more may be used, and 3-20 carbons isa preferred range. Materials with asymmetric structures may have bettersolution processibility than those having symmetric structures, becauseasymmetric materials may have a lower tendency to recrystallize.Dendrimer substituents may be used to enhance the ability of smallmolecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention maybe incorporated into a wide variety of consumer products, including flatpanel displays, computer monitors, televisions, billboards, lights forinterior or exterior illumination and/or signaling, heads up displays,fully transparent displays, flexible displays, laser printers,telephones, cell phones, personal digital assistants (PDAs), laptopcomputers, digital cameras, camcorders, viewfinders, micro-displays,vehicles, a large area wall, theater or stadium screen, or a sign.Various control mechanisms may be used to control devices fabricated inaccordance with the present invention, including passive matrix andactive matrix. Many of the devices are intended for use in a temperaturerange comfortable to humans, such as 18 degrees C. to 30 degrees C., andmore preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications indevices other than OLEDs. For example, other optoelectronic devices suchas organic solar cells and organic photodetectors may employ thematerials and structures. More generally, organic devices, such asorganic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl,heterocyclic group, aryl, aromatic group, and heteroaryl are known tothe art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32,which are incorporated herein by reference.

Carbene iridium complexes are new class of phosphorescent dopantmaterials, which can provide various colors when used as emissivedopants in an OLED device. An overwhelming majority of N heterocycliccarbenes (NHC) ligands are derived from the imidazole (C₃H₄N₂)framework. As research in NHC carbene metal complexes in OLEDs continuesto advance at a vigorous pace, there is a strong need to develop otherheterocyclic systems that can be adapted to the demands of differentOLED materials. In particular, compounds in which one of the N atoms inan imidazole is replaced with an O atom to form an oxazole or with an Satom to form a thioazole are provided herein (as illustrated in FIG. 3).Additionally, a novel methodology to synthesize heterocyclic carbenemetal complexes is provided. These compounds may lead to unique deviceproperties in OLEDs, including improved stability and improvedcolor-tuning.

There are many beneficial features of the heterocyclic carbene metalcomplexes provided herein, including a reducible carbene moiety, i.e.,reversible reduction, short excited state lifetime and a novel ligationmethod. First, imidazole-based carbene metal complexes generally do nothave reversible reduction by CV measurement. In general, imidazole-basedcarbenes have a high LUMO that is difficult to reduce. This can lead toextremely high LUMO and electron instability. The oxazole and thioazoleheterocyclic-based carbene metal complexes provided herein havereversible reduction and a shallow LUMO. Without being bound by theory,it is believed that the reversible reduction may improve the electronstability of these compounds when used as a dopant. By using the oxazoleand thioazole heterocyclic carbenes configuration, the carbene moietymay become more reducible. With a N-containing aromatic ring fused intothis heterocyclic carbene ring, the LUMO level may be further reduced.In other words, it may be easier to lower the LUMO of oxazole andthioazole heterocyclic carbenes compared to imidazole-based carbenes,which may allow for better device stability.

Second, iridium carbene complexes generally have a long excited statelifetime due to poor MLCT mixing. The oxazole and thioazole heterocycliccarbene metal complexes provided herein, however, may have shorterexcited state lifetimes. Fusion of a N-containing aromatic ring to thisheterocyclic carbene ring is not expected to alter the shortened excitedstate lifetime demonstrated by these compounds.

Third, the traditional ligation method via Ag₂O fails for theseheterocyclic based carbene metal complexes. These heterocyclic carbenesare more difficult to attach to metals than their correspondingimidazole carbene counterparts. Therefore, a new ligation method viacopper carbene complexes has been developed. The free carbene stabilityfor N, S-based carbenes is worse than conventional imidazole-basedcarbenes due to the lack of steric protection. Without being bound bytheory, it is believed that the conventional transmetallation via Ag₂Owas not successful for the oxazole and thioazole heterocyclic carbenesbecause the oxazole and thioazole free carbene is less stable thanimidazole carbene due to less steric protection for the carbene centerin the oxazole and thioazole carbenes. The novel method developed forsynthesis of these heterocyclic carbene complexes includes reacting acarbene precursor salt with copper-t-butoxide to yield a cooperdichloride carbene dimer, which is then transmetallated to a metalprecursor to yield heterocyclic carbene metal complexes. In particular,the method may be used to make tris heterocyclic carbene metalcomplexes.

Heterocyclic carbene metal complexes are provided. The compoundscomprise a ligand L having the structure:

X₁ is S or O. X₂, X₃, X₄, and X₅ are independently C or N. At least oneof X₂, X₃, X₄, and X₅ is N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. Preferably, A is benzene.The ligand L is coordinated to a transition metal M having an atomicnumber greater than 40. Preferably, the metal M is Ir or Os. Morepreferably, the metal M is Ir. Additionally, the metal M is preferablyOs. The bidentate ligand L may be linked with other ligands to comprisea tridentate, tetradentate, pentadentate or hexadentate ligand.

In one aspect, the ligand has the formula:

At least one of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In another aspect, the ligand has the formula:

At least two of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In one aspect, the compound is heteroleptic. In another aspect, thecompound is homoleptic. In yet another aspect, the compound has theformula:

Specific examples of the heterocyclic carbene compounds are provided. Inone aspect, the compound is selected from the group consisting of:

Each X₁ is independently S or O.

Additional specific examples of heterocyclic carbene compounds areprovided. In one aspect, the compound is selected from the groupconsisting of:

Additionally, a first device comprising an organic light emitting deviceis provided. The organic light emitting device further comprises ananode, a cathode, and an organic layer, disposed between the anode andthe cathode. The organic layer comprises a compound comprising a ligandL having the structure:

X₁ is S or O. X₂, X₃, X₄, and X₅ are independently C or N. At least oneof X₂, X₃, X₄, and X₅ is N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. Preferably, A is benzene.The ligand L is coordinated to a transition metal M having an atomicnumber greater than 40. Preferably, the metal M is Ir or Os. Morepreferably, the metal M is Os. More preferably, the metal M is Ir. Thebidentate ligand may be linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

In one aspect, the ligand has the formula:

At least one of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In another aspect, the ligand has the formula:

At least two of X₂, X₃, X₄, and X₅ is N. R₂ may represent mono, di, trior tetra substitutions. R₂ is independently selected from the groupconsisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. Two adjacent substituentsof R₂ are optionally joined to form a fused ring.

In one aspect, the compound is heteroleptic. In another aspect, thecompound is homoleptic. In yet another aspect, the homoleptic compoundhas the formula:

Specific examples of compounds that may be used in the device areprovided. In one aspect, the compound is selected from the groupconsisting of Compound 1G-Compound 28G. Each X₁ is independently S or O.

In another aspect, the compound is selected from the group consisting ofCompound 1-Compound 20.

In one aspect, the organic layer is an emissive layer and the compoundis an emissive dopant. In another aspect, the organic layer furthercomprises a host. Preferably, the host is a compound that comprises atleast one of the chemical groups selected from the group consisting of:

Each of R′″₁, R′″₂, R′″₃, R′″₄, R′″₅, R′″₆ and R′″₇ are independentlyselected from the group consisting of hydrogen, deuterium, alkyl,alkoxy, amino, alkenyl, alkynyl, arylalkyl, heteroalkyl, aryl andheteroaryl. k is an integer from 0 to 20. Each of X¹, X², X³, X⁴, X⁵,X⁶, X⁷ and X⁸ are independently selected from the group consisting of CHand N.

In another aspect, the host is a metal complex. In yet another aspect,the metal complex is selected from the group consisting of:

(O—N) is a bidentate ligand having metal coordinated to atoms O and N. Lis an ancillary ligand. m is an integer value from 1 to the maximumnumber of ligands that may be attached to the metal.

In one aspect, the first device is a consumer product. In anotheraspect, the first device is an organic light emitting device.

A process for making a carbene metal complex is also provided. Theprocess comprises reacting the copper dichloride carbene dimer with ametal precursor to yield the carbene metal complex. In one aspect, theprocess further comprises reacting a carbene salt with copper-t-butoxideto yield a copper dichloride carbene dimer, prior to reacting the copperdichloride carbene dimer with the metal precursor.

In one aspect, the metal is Ir, Os, Ru or Pt. In another aspect, themetal precursor is selected from the group consisting of [IrCl(COD)]₂,OsCl₂(DMSO)₄, RuCl₂(DMSO)₄, and PtCl₂(SEt₂)₂.

In one aspect, the carbene metal complex has the formula:

X₁ is NR_(B), S or O. In one aspect, X₁ is NR_(B). In another aspect, X₁is S. In yet another aspect, X₁ is O. X₂, X₃, X₄, and X₅ areindependently C or N. R₁ may represent mono, di, tri or tetrasubstitutions. R₁ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents of R₁ are optionallyjoined to form a fused ring. R_(A) may represent mono, di, tri, or tetrasubstitutions. R_(A) is independently selected from the group consistingof hydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl,arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl,heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylicacids, ester, nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl,phosphino, and combinations thereof. Two adjacent substituents of R_(A)are optionally joined to form a fused ring. A is a 5-membered or6-membered carbocyclic or heterocyclic ring. R_(B) is selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof. The ligand L iscoordinated to a transition metal M having an atomic number greater than40. The bidentate ligand may be linked with other ligands to comprise atridentate, tetradentate, pentadentate or hexadentate ligand.

In one aspect, the carbene metal complex is heteroleptic. In anotheraspect, the carbene metal complex is homoleptic. Preferably, the carbenemetal complex is tris.

Combination with Other Materials

The materials described herein as useful for a particular layer in anorganic light emitting device may be used in combination with a widevariety of other materials present in the device. For example, emissivedopants disclosed herein may be used in conjunction with a wide varietyof hosts, transport layers, blocking layers, injection layers,electrodes and other layers that may be present. The materials describedor referred to below are non-limiting examples of materials that may beuseful in combination with the compounds disclosed herein, and one ofskill in the art can readily consult the literature to identify othermaterials that may be useful in combination.

HIL/HTL:

A hole injecting/transporting material to be used in the presentinvention is not particularly limited, and any compound may be used aslong as the compound is typically used as a hole injecting/transportingmaterial. Examples of the material include, but not limit to: aphthalocyanine or porphyrin derivative; an aromatic amine derivative; anindolocarbazole derivative; a polymer containing fluorohydrocarbon; apolymer with conductivity dopants; a conducting polymer, such asPEDOT/PSS; a self-assembly monomer derived from compounds such asphosphonic acid and sliane derivatives; a metal oxide derivative, suchas MoO_(x); a p-type semiconducting organic compound, such as1,4,5,8,9,12-Hexaazatriphenylenehexacarbonitrile; a metal complex, and across-linkable compounds.

Examples of aromatic amine derivatives used in HIL or HTL include, butnot limit to the following general structures:

Each of Ar¹ to Ar⁹ is selected from the group consisting aromatichydrocarbon cyclic compounds such as benzene, biphenyl, triphenyl,triphenylene, naphthalene, anthracene, phenalene, phenanthrene,fluorene, pyrene, chrysene, perylene, azulene; group consisting aromaticheterocyclic compounds such as dibenzothiophene, dibenzofuran,dibenzoselenophene, furan, thiophene, benzofuran, benzothiophene,benzoselenophene, carbazole, indolocarbazole, pyridylindole,pyrrolodipyridine, pyrazole, imidazole, triazole, oxazole, thiazole,oxadiazole, oxatriazole, dioxazole, thiadiazole, pyridine, pyridazine,pyrimidine, pyrazine, triazine, oxazine, oxathiazine, oxadiazine,indole, benzimidazole, indazole, indoxazine, benzoxazole, benzisoxazole,benzothiazole, quinoline, isoquinoline, cinnoline, quinazoline,quinoxaline, naphthyridine, phthalazine, pteridine, xanthene, acridine,phenazine, phenothiazine, phenoxazine, benzofuropyridine,furodipyridine, benzothienopyridine, thienodipyridine,benzoselenophenopyridine, and selenophenodipyridine; and groupconsisting 2 to 10 cyclic structural units which are groups of the sametype or different types selected from the aromatic hydrocarbon cyclicgroup and the aromatic heterocyclic group and are bonded to each otherdirectly or via at least one of oxygen atom, nitrogen atom, sulfur atom,silicon atom, phosphorus atom, boron atom, chain structural unit and thealiphatic cyclic group. Wherein each Ar is further substituted by asubstituent selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof. Two adjacent substituents are optionally joined to form a fusedring.

In one aspect, Ar¹ to Ar⁹ is independently selected from the groupconsisting of:

k is an integer from 1 to 20; X¹ to X⁸ is CH or N; Ar¹ has the samegroup defined above.

Examples of metal complexes used in HIL or HTL include, but not limit tothe following general formula:

M is a metal, having an atomic weight greater than 40; (Y¹-Y²) is abidentate ligand, Y1 and Y² are independently selected from C, N, O, P,and S; L is an ancillary ligand; m is an integer value from 1 to themaximum number of ligands that may be attached to the metal; and m+n isthe maximum number of ligands that may be attached to the metal.

In one aspect, (Y¹-Y²) is a 2-phenylpyridine derivative.

In another aspect, (Y¹-Y²) is a carbene ligand.

In another aspect, M is selected from Ir, Pt, Os, and Zn.

In a further aspect, the metal complex has a smallest oxidationpotential in solution vs. Fc⁺/Fc couple less than about 0.6 V.

Host:

The light emitting layer of the organic EL device of the presentinvention preferably contains at least a metal complex as light emittingmaterial, and may contain a host material using the metal complex as adopant material. Examples of the host material are not particularlylimited, and any metal complexes or organic compounds may be used aslong as the triplet energy of the host is larger than that of thedopant.

Examples of metal complexes used as host are preferred to have thefollowing general formula:

M is a metal; (Y³-Y⁴) is a bidentate ligand, Y³ and Y⁴ are independentlyselected from C, N, O, P, and S; L is an ancillary ligand; m is aninteger value from 1 to the maximum number of ligands that may beattached to the metal; and m+n is the maximum number of ligands that maybe attached to the metal.

In one aspect, the metal complexes are:

(O—N) is a bidentate ligand, having metal coordinated to atoms O and N.

In another aspect, M is selected from Ir and Pt.

In a further aspect, (Y³-Y⁴) is a carbene ligand.

Examples of organic compounds used as host are selected from the groupconsisting aromatic hydrocarbon cyclic compounds such as benzene,biphenyl, triphenyl, triphenylene, naphthalene, anthracene, phenalene,phenanthrene, fluorene, pyrene, chrysene, perylene, azulene; groupconsisting aromatic heterocyclic compounds such as dibenzothiophene,dibenzofuran, dibenzoselenophene, furan, thiophene, benzofuran,benzothiophene, benzoselenophene, carbazole, indolocarbazole,pyridylindole, pyrrolodipyridine, pyrazole, imidazole, triazole,oxazole, thiazole, oxadiazole, oxatriazole, dioxazole, thiadiazole,pyridine, pyridazine, pyrimidine, pyrazine, triazine, oxazine,oxathiazine, oxadiazine, indole, benzimidazole, indazole, indoxazine,benzoxazole, benzisoxazole, benzothiazole, quinoline, isoquinoline,cinnoline, quinazoline, quinoxaline, naphthyridine, phthalazine,pteridine, xanthene, acridine, phenazine, phenothiazine, phenoxazine,benzofuropyridine, furodipyridine, benzothienopyridine,thienodipyridine, benzoselenophenopyridine, and selenophenodipyridine;and group consisting 2 to 10 cyclic structural units which are groups ofthe same type or different types selected from the aromatic hydrocarboncyclic group and the aromatic heterocyclic group and are bonded to eachother directly or via at least one of oxygen atom, nitrogen atom, sulfuratom, silicon atom, phosphorus atom, boron atom, chain structural unitand the aliphatic cyclic group. Wherein each group is furthersubstituted by a substituent selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents are optionally joined toform a fused ring.

In one aspect, host compound contains at least one of the followinggroups in the molecule:

R¹ to R⁷ is independently selected from the group consisting ofhydrogen, deuterium, halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl,alkoxy, aryloxy, amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl,alkynyl, aryl, heteroaryl, acyl, carbonyl, carboxylic acids, ester,nitrile, isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, andcombinations thereof. Two adjacent substituents are optionally joined toform a fused ring. When it is aryl or heteroaryl, it has the similardefinition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

HBL:

A hole blocking layer (HBL) may be used to reduce the number of holesand/or excitons that leave the emissive layer. The presence of such ablocking layer in a device may result in substantially higherefficiencies as compared to a similar device lacking a blocking layer.Also, a blocking layer may be used to confine emission to a desiredregion of an OLED.

In one aspect, compound used in HBL contains the same molecule used ashost described above.

In another aspect, compound used in HBL contains at least one of thefollowing groups in the molecule:

k is an integer from 0 to 20; L is an ancillary ligand, m is an integerfrom 1 to 3.

ETL:

Electron transport layer (ETL) may include a material capable oftransporting electrons. Electron transport layer may be intrinsic(undoped), or doped. Doping may be used to enhance conductivity.Examples of the ETL material are not particularly limited, and any metalcomplexes or organic compounds may be used as long as they are typicallyused to transport electrons.

In one aspect, compound used in ETL contains at least one of thefollowing groups in the molecule:

R¹ is selected from the group consisting of hydrogen, deuterium, halide,alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy, amino,silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl,acyl, carbonyl, carboxylic acids, ester, nitrile, isonitrile, sulfanyl,sulfinyl, sulfonyl, phosphino, and combinations thereof. Two adjacentsubstituents are optionally joined to form a fused ring. When it is arylor heteroaryl, it has the similar definition as Ar's mentioned above.

Ar¹ to Ar³ has the similar definition as Ar's mentioned above.

k is an integer from 0 to 20.

X¹ to X⁸ is selected from CH or N.

In another aspect, the metal complexes used in ETL contains, but notlimit to the following general formula:

(O—N) or (N—N) is a bidentate ligand, having metal coordinated to atomsO, N or N, N; L is an ancillary ligand; m is an integer value from 1 tothe maximum number of ligands that may be attached to the metal.

In any above-mentioned compounds used in each layer of OLED device, thehydrogen atoms can be partially or fully deuterated.

In addition to and/or in combination with the materials disclosedherein, many hole injection materials, hole transporting materials, hostmaterials, dopant materials, exiton/hole blocking layer materials,electron transporting and electron injecting materials may be used in anOLED. Non-limiting examples of the materials that may be used in an OLEDin combination with materials disclosed herein are listed in Table 1below. Table 1 lists non-limiting classes of materials, non-limitingexamples of compounds for each class, and references that disclose thematerials.

TABLE 1 MATERIAL EXAMPLES OF MATERIAL PUBLICATIONS Hole injectionmaterials Phthalocyanine and porphryin compounds

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J. Lumin. 72-74, 985 (1997) CF_(x) Fluorohydrocarbon polymer

Appl. Phys. Lett. 78, 673 (2001) Conducting polymers (e.g., PEDOT:PSS,polyaniline, polypthiophene)

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US20030162053 Triarylamine or polythiophene polymers with conductivitydopants

EA01725079A1 and

Arylamines complexed with metal oxides such as molybdenum and tungstenoxides

SID Symposium Digest, 37, 923 (2006) WO2009018009 Semiconducting organiccomplexes

US20020158242 Metal organometallic complexes

US20060240279 Cross-linkable compounds

US20080220265 Hole transporting materials Triarylamines (e.g., TPD,α-NPD)

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U.S. Pat. No. 5,061,569

EP650955

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Adv. Mater. 6, 677 (1994), US20080124572 Triarylamine with(di)benzothiophene/ (di)benzofuran

US20070278938, US20080106190 Indolocarbazoles

Synth. Met. 111, 421 (2000) Isoindole compounds

Chem. Mater. 15, 3148 (2003) Metal carbene complexes

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Appl. Phys. Lett. 78, 1622 (2001) Metal 8-hydroxyquinolates (e.g., Alq₃,BAlq)

Nature 395, 151 (1998)

US20060202194

WO2005014551

WO2006072002 Metal phenoxybenzothiazole compounds

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Org. Electron. 1, 15 (2000) Aromatic fused rings

WO2009066779, WO2009066778, WO2009063833, US20090045731, US20090045730,WO2009008311, US20090008605, US20090009065 Zinc complexes

WO2009062578 Green hosts Arylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001)

US20030175553

WO2001039234 Aryltriphenylene compounds

US20060280965

US20060280965

WO2009021126 Donor acceptor type molecules

WO2008056746 Aza- carbazole/DBT/DBF

JP2008074939 Polymers (e.g., PVK)

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WO2004093207 Metal phenoxybenzooxazole compounds

WO2005089025

WO2006132173

JP200511610 Spirofluorene- carbazole compounds

JP2007254297

JP2007254297 Indolocabazoles

WO2007063796

WO2007063754 5-member ring electron deficient heterocycles (e.g.,triazole, oxadiazole)

J. Appl. Phys. 90, 5048 (2001)

WO2004107822 Tetraphenylene complexes

US20050112407 Metal phenoxypyridine compounds

WO2005030900 Metal coordination complexes (e.g., Zn, Al withN{circumflex over ( )}N ligands)

US20040137268, US20040137267 Blue hosts Arylcarbazoles

Appl. Phys. Lett, 82, 2422 (2003)

US20070190359 Dibenzothiophene/ Dibenzofuran-carbazole compounds

WO2006114966, US20090167162

US20090167162

WO2009086028

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WO2009003898 Silicon/Germanium aryl compounds

EP2034538A Aryl benzoyl ester

WO2006100298 High triplet metal organometallic complex

U.S. Pat. No. 7,154,114 Phosphorescent dopants Red dopants Heavy metalporphyrins (e.g., PtOEP)

Nature 395, 151 (1998) Iridium(III) organometallic complexes

Appl. Phys. Lett. 78, 1622 (2001)

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US20070087321

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WO2009100991

WO2008101842 Platinum(II) organometallic complexes

WO2003040257 Osminum(III) complexes

Chem. Mater. 17, 3532 (2005) Ruthenium(II) complexes

Adv. Mater. 17, 1059 (2005) Rhenium (I), (II), and (III) complexes

US20050244673 Green dopants Iridium(III) organometallic complexes

Inorg. Chem. 40, 1704 (2001) and its derivatives

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U.S. Pat. No. 7,332,232

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US20090039776

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US20070190359

US20060008670 JP2007123392

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Angew. Chem. Int. Ed. 2006, 45, 7800

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US20090165846

US20080015355 Monomer for polymeric metal organometallic compounds

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Appl. Phys. Lett. 86, 153505 (2005)

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WO2009000673 Gold complexes

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US20030138657 Organometallic complexes with two or more metal centers

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Chem. Mater. 18, 5119 (2006)

Inorg. Chem. 46, 4308 (2007)

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WO2006098120, WO2006103874 Exciton/hole blocking layer materialsBathocuprine compounds (e.g., BCP, BPhen)

Appl. Phys. Lett. 75, 4 (1999)

Appl. Phys. Lett. 79, 449 (2001) Metal 8-hydroxyquinolates (e.g., BAlq)

Appl. Phys. Lett. 81, 162 (2002) 5-member ring electron deficientheterocycles such as triazole, oxadiazole, imidazole, benzoimidazole

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EXPERIMENTAL Compound Examples Example 1

Synthesis of 2-(methylthio)-N-Phenylpyridine-3amino

3-bromo-2(methylthio)pyridine (25 g, 123 mmol), Pd₂dba₃ (6.75 g, 7.38mmol), S-Phos (6.06 g, 14.77 mmol) and sodium butan-1-olate (17.74 g,185 mmol) are placed in dry 3-neck flask under N₂. The reaction mixtureis vacuumed and charged with N₂ a total of three times. Aniline (22.93g, 246 mmol) and 500 mL toluene are added to the reaction mixture. Thereaction mixture is refluxed for 18 h. The crude reaction mixture is runthrough silica gel plug and eluted with toluene. The toluene portion isconcentrated down and subjected to silica gel column using 3-5% DCM inHexane to yield the desired product.

Synthesis of 3-(phenylamino)pyridine-2-thiol

A 250 mL round bottom flask is charged with sodium methanethiolate (5.18g, 73.8 mmol), 2-(methylthio)-N-Phenylpyridine-3amino (13.25 g, 61.5mmol) and Hexamethyl phosphoramide (HMPA) (100 mL). The reaction mixtureis heated up to 100° C. for 7 h. The reaction is cooled to roomtemperature, and 100 mL of 1N HCl is added. The reaction mixture isextracted with 3×100 mL ethyl acetate. The organic portion is washedwith 3×50 mL Brien, and then dried over sodium sulfate and evaporated toyield the desired compound.

Synthesis of Benzothioazole Carbene Ligand Precursor

A 250 mL round bottom flask was charged with zinc dust (2.339 g, 35.8mmol), 3-(phenylamino)pyridine-2-thiol (12 g, 59.6 mmol) and Formic Acid(100 mL). The reaction mixture is refluxed under N₂ for 6 h. Thereaction mixture is filtered off to get rid of insoluble material.Hypochloric acid (35.9 mL, 59.9 mmol) is added to the filtrate andstirred for 20 minutes. 200 mL of water is added and the precipitationis collected. The precipitation is washed with H₂O and Ether to yieldthe desired product.

Synthesis of Dichloro Copper Dimer

A 500 mL round bottom flask is charged with CuCl (3.9 g, 39.4 mmol),Lithium tert-butoxide (3.15 g, 39.4 mmol) and anhydrous THF (400 mL).The reaction mixture is stirred inside the glove box overnight.Perchloride salt (2.31 g, 7.41 mmol) is added into the reaction mixtureand stirred overnight. The reaction mixture is removed from glove boxand filtered. The filtrate is concentrated to dryness, and re-suspendedin dichloromethane. The suspension is filtered, and the filtrate isconcentrated to dryness to yield the desired compound.

Synthesis of Benzothioazole Iridium Tris Complex

A 500 mL round bottom flask is charged with copper dichloride bridgedimer (1.68 g, 2.71 mmol), Iridium COD dimer (0.568 g, 0.846 mmol) andchlorobenzene (300 mL) to give an orange suspension. The reactionmixture is vacuumed and back filled with N₂ a total of three times.Then, the reaction mixture is heated to reflux overnight. The reactionmixture is filtered, and the filtrate is concentrated to dryness. Theresidue is subjected to column chromatography (SiO₂, 100% DCM) to yieldthe desired compound.

Example 2

Synthesis of 3-methoxy-N-phenylpyridine-2amine

A 1 L 3-neck flask is charged with 3-methoxypyridine-2-amine (17.65 g,143 mmol), bromobenzene (15 g, 96 mmol), Pd₂DBA₃ (1.75 g, 1.91 mmol),Sodium tert-butoxide (18.36 g, 101 mmol), S-Phos (1.56 g, 3.82 mmole)and 400 mL of xylene. The reaction mixture is refluxed for 4 h. Theproduct is isolated by column chromatography (5% EtoAc in Hexs) to yieldthe desired product.

Synthesis of 2-(phenylamino)pyridine-3-ol

A 1 L 3-neck flask is charged with Pyridinium chloride (52.2 g, 452mmol) and 3-methoxy-N-phenylpyridine-2amine (9 g, 45.2 mmol). Thereaction mixture is heated to 200° C. for 4 h. The reaction mixture isdumped into 5% HCl (200 mL), and extracted with 3×300 mL ETOAC. Theorganic portion is combined and purified by column chromatography (100%DCM) to yield the desired product.

Synthesis of Benzooxoazole Carbene Ligand Precursor

Hydrogen tetrafluoroborate (6.79 mL, 48% w/w) is added drop-wise to asolution of 2-(phenylamino)pyridine-3-ol (9 g, 48.6 mmol) in 30 mLMethanol. After 30 minutes of stirring, the solvent is removed undervacuum and 30 mL (EtO)₃CH is added. The resulting solution is stirred atroom temperature under N₂ overnight to give a white suspension. Thesolid is filtered, and then washed with diethyl ether to give theproduct.

Synthesis of Benzooxazole Iridium Tris Complex

For synthesis of benzooxazole iridium tris complex, please refer to thebenzothioazole example.

Example 3

Synthesis of N¹,N³-bis(2-(methylthio)pyridine-3-yl)benzene-1,3-diamine

3-bromo-2(methylthio)pyridine (25 g, 123 mmol), Pd₂dba₃ (6.75 g, 7.38mmol), S-Phos (6.06 g, 14.77 mmole) and sodium butan-1-olate (17.74 g,185 mmol) are placed in dry 3-neck flask under N₂. The reaction mixtureis vacuumed, and charged with N₂ for a total of three times.1,3-diaminobenzene (6.64 g, 61.5 mmol) and 500 mL toluene are added tothe reaction mixture. The reaction mixture is refluxed for 18 h. Thecrude reaction mixture is run through a silica gel plug and eluted withtoluene. The toluene portion is concentrated down and subjected to asilica gel column using 3-5% DCM in Hexane to yield the desired product.

Synthesis of 3,3(1,3-phenylenebis(azanediyl))bis(pyridine-2-thiol)

A 250 ml, round bottom flask is charged with sodium methanethiolate(5.18 g, 73.8 mmol),N¹,N³-bis(2-(methylthio)pyridine-3-yl)benzene-1,3-diamine (13.25 g, 61.5mmol) and Hexamethyl phosphoramide(HMPA) (100 mL). The reaction mixtureis heated up to100° C. for 7 h. The reaction is cooled to roomtemperature, and 100 mL of 1N HCl is added. The reaction mixture isextracted with 3×100 mL ethyl acetate. The organic portion is washedwith 3×50 mL Brien, dried over sodium sulfate and evaporated to yieldthe desired compound.

Synthesis of 1,1′-(1,3-phenylene)bis(thiazolo[5,4-b]pyridine-1-ium)Perchlorate salt

A 250 mL round bottom flask is charged with zinc dust (2.339 g, 35.8mmol), 3,3′-(1,3-phenylenebis(azanediyl))bis(pyridine-2-thiol) andFormic Acid (100 mL). The reaction mixture is refluxed under N₂ for 6 h.The reaction mixture is filtered off to get rid of insoluble material.Hypochloric acid (35.9 mL, 59.9 mmol) is added to the filtrate andstirred for 20 minutes. 200 mL of water is added and the precipitationis collected. The precipitation is washed with H₂O and Ether to yieldthe desired product.

Synthesis of Copper Carbene Complex

A 500 mL round bottom flask is charged with CuCl (3.9 g, 39.4 mmol),Lithium tert-butoxide (3.15 g, 39.4 mmol) and anhydrous THF (400 mL).The reaction mixture is stirred inside the glove box overnight. Theperchloride salt (4.05 g, 7.41 mmol) is added into the reaction mixtureand stirred overnight. The reaction mixture is removed from the glovebox, and filtered. The filtrate is concentrated to dryness andre-suspended in dichloromethane. The suspension is filtered and filtrateis concentrated to dryness to yield the desired compound.

Synthesis of Osmium Carbene Complex

A 250 mL round-bottomed flask is charged with OsCl₂(DMSO)₄ (250 mg,0.436 mmol), copper carbene complex (584 mg, 1.3 mmol) in2-ethoxyethanol (125 mL) to give a tan suspension. The reaction mixtureis vacuumed and back filled with N₂; then the reaction mixture is heatedto reflux for 1 h. The reaction mixture is filtered though celite, andthe filtrate is subject to column chromatography (SiO₂, Et₃N pretreated,60% EtOAC in hexanes) to yield the desired compound.

It is understood that the various embodiments described herein are byway of example only, and are not intended to limit the scope of theinvention. For example, many of the materials and structures describedherein may be substituted with other materials and structures withoutdeviating from the spirit of the invention. The present invention asclaimed may therefore includes variations from the particular examplesand preferred embodiments described herein, as will be apparent to oneof skill in the art. It is understood that various theories as to whythe invention works are not intended to be limiting.

1. A compound comprising a ligand L having the structure:

wherein X₁ is S or O; wherein X₂, X₃, X₄, and X₅ are independently C orN; wherein at least one of X₂, X₃, X₄, and X₅ is N; wherein R₁ mayrepresent mono, di, tri or tetra substitutions; wherein R₁ isindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; wherein two adjacent substituents of R₁ are optionally joinedto form a fused ring; wherein R_(A) may represent mono, di, tri, ortetra substitutions; wherein R_(A) is independently selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein two adjacentsubstituents of R_(A) are optionally joined to form a fused ring;wherein A is a 5-membered or 6-membered carbocyclic or heterocyclicring; wherein the ligand L is coordinated to a metal M selected from Irand Os; and wherein the bidentate ligand may be linked with otherligands to comprise a tridentate, tetradentate, pentadentate orhexadentate ligand.
 2. The compound of claim 1, wherein A is benzene. 3.The compound of claim 1, wherein the ligand has the formula:

wherein at least one of X₂, X₃, X₄, and X₅ is N; wherein R₂ mayrepresent mono, di, tri or tetra substitutions; wherein R₂ isindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; and wherein two adjacent substituents of R₂ are optionallyjoined to form a fused ring.
 4. The compound of claim 1, wherein theligand has the formula:

wherein at least two of X₂, X₃, X₄, and X₅ is N; wherein R₂ mayrepresent mono, di, tri or tetra substitutions; wherein R₂ isindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; and wherein two adjacent substituents of R₂ are optionallyjoined to form a fused ring.
 5. The compound of claim 1, wherein thecompound is heteroleptic.
 6. The compound of claim 1, wherein thecompound is homoleptic.
 7. The compound of claim 1, wherein the compoundhas the formula:


8. The compound of claim 1, wherein the compound is selected from thegroup consisting of:

wherein each X₁ is independently S or O.
 9. The compound of claim 1,wherein the compound is selected from the group consisting of:


10. The compound of claim 1, wherein the compound has the formula:


11. A first device comprising an organic light emitting device, furthercomprising: an anode; a cathode; and an organic layer, disposed betweenthe anode and the cathode, comprising a compound comprising a ligand Lhaving the structure:

wherein X₁ is S or O; wherein X₂, X₃, X₄, and X₅ are independently C orN; wherein at least one of X₂, X₃, X₄, and X₅ is N; wherein R₁ mayrepresent mono, di, tri or tetra substitutions; wherein R₁ isindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; wherein two adjacent substituents of R₁ are optionally joinedto form a fused ring; wherein R_(A) may represent mono, di, tri, ortetra substitutions; wherein R_(A) is independently selected from thegroup consisting of hydrogen, deuterium, halide, alkyl, cycloalkyl,heteroalkyl, arylalkyl, alkoxy, aryloxy, amino, silyl, alkenyl,cycloalkenyl, heteroalkenyl, alkynyl, aryl, heteroaryl, acyl, carbonyl,carboxylic acids, ester, nitrile, isonitrile, sulfanyl, sulfinyl,sulfonyl, phosphino, and combinations thereof; wherein two adjacentsubstituents of R_(A) are optionally joined to form a fused ring;wherein A is a 5-membered or 6-membered carbocyclic or heterocyclicring; wherein the ligand L is coordinated to a metal M selected from Jrand Os; and wherein the bidentate ligand may be linked with otherligands to comprise a tridentate, tetradentate, pentadentate orhexadentate ligand.
 12. The first device of claim 11, wherein theorganic layer is an emissive layer and the compound is an emissivedopant.
 13. The first device of claim 11, wherein the organic layerfurther comprises a host.
 14. The first device of claim 13, wherein thehost is a compound that comprises at least one of the chemical groupsselected from the group consisting of:

wherein each of R′″₁, R′″₂, R′″₃, R′″₄, R′″₅, R′″₆ and R′″₇ areindependently selected from the group consisting of hydrogen, deuterium,halide, alkyl, cycloalkyl, heteroalkyl, arylalkyl, alkoxy, aryloxy,amino, silyl, alkenyl, cycloalkenyl, heteroalkenyl, alkynyl, aryl,heteroaryl, acyl, carbonyl, carboxylic acids, ester, nitrile,isonitrile, sulfanyl, sulfinyl, sulfonyl, phosphino, and combinationsthereof; wherein two adjacent substituents are optionally joined to forma fused ring; wherein k is an integer from 0 to 20; and wherein each ofX¹, X², X³, X⁴, X⁵, X⁶, X⁷ and X⁸ are independently selected from thegroup consisting of CH and N.
 15. The first device of claim 13, whereinthe host is a metal complex.
 16. The first device of claim 15, whereinthe metal complex is selected from the group consisting of:

wherein (O—N) is a bidentate ligand having metal coordinated to atoms Oand N; wherein L is an ancillary ligand; and wherein m is an integervalue from 1 to the maximum number of ligands that may be attached tothe metal.
 17. A process for making a carbene metal complex, comprising:reacting a copper dichloride carbene dimer with a metal precursor toyield the carbene metal complex.
 18. The process of claim 17, furthercomprising reacting a carbene salt with copper-t-butoxide to yield acopper dichloride carbene dimer, prior to reacting the copper dichloridecarbene dimer with the metal precursor.
 19. The process of claim 17,wherein the metal is Ir, Os, Ru or Pt.
 20. The process of claim 19,wherein the metal precursor is selected from the group consisting of[IrCl(COD)]₂, OsCl₂(DMSO)₄, RuCl₂(DMSO)₄, and PtCl₂(SEt₂)₂.